predominantly of short sedges. In their core area, the river valleys of the Biebrza in Poland and the Pripyat in Belarus, large wetlands remain, but the decline has still been dramatic. There, it’s not so much habitat loss as habitat change, prompted by socioeconomic factors, that’s been the problem. The Aquatic Warbler’s favoured sedge-beds, traditionally scythed by hand for hay and thatch, have been abandoned by an urbanising population. Scrub, previously kept in check, has taken over and sedge-beds have dried out, allowing reed to become dominant. Traditional hand scything had largely ceased in these areas by the 1990s – Aquatic Warblers in their last stronghold were in trouble. A massive conservation effort was needed, combining both scientific research as well as on the ground habitat management. Recently, a machine has been developed that replicates the effects of handscything. This can be used to cut large swathes of marsh effectively, without slicing off the low sedge-tussocks that the birds nest on. Such practical habitat management, combined with research by conservation scientists, has stabilised the core population, which is now thought to consist of about 12,000 singing males.
Knowledge gaps filled
As a result of this extensive work, some large gaps in our knowledge of the Aquatic Warbler have been filled. For example, until 2007 it still wasn’t known where birds spent the winter. It is very hard to conserve a species when you don’t know where it spends the majority its life. The process that finally led to birds being seen in the field in Senegal is fascinating. Molecular analysis has helped massively to determine the movements and trace the origins of migratory animals. The molecular composition, specifically the heavy isotope composition, of rain differs across the globe; if you were to give the right scientist a rainwater sample, they’d be able to tell you where on the planet it fell. Animals incorporate this ‘isotopic signature’ into their body tissues, through diet. Because Aquatic Warblers regrow their flight-feathers in Aquatic Warblers look, in some ways, like a cross between a Sedge Warbler and a particularly streaky Grasshopper Warbler winter, feather samples taken during the summer in eastern Europe could be analysed in the hope of revealing their wintering grounds. So it proved, when the samples were compared with isotopic profile maps of West Africa a specific location was identified: The Djoudj National Park in Senegal. Birds were then searched for, and seen in the field, within this park, and more recently other wintering sites at smaller wetlands in Mauritania and Mali have been discovered. Unfortunately, the construction of a river dam further upstream of the Djoudj, has resulted in both the quality and quantity of habitat reducing substantially. As with many of our summer migrants, it’s a two pronged attack, with both breeding and wintering habitats becoming degraded. If Aquatic Warblers are flying from eastern Europe to Senegal in autumn, why are they ending up in wetlands on the south coast of England? Unlike other passerines heading to Africa in autumn, that take a more direct southerly route, Aquatic Warblers on leaving their breeding grounds travel westward. They appear to orientate themselves by tracking the coastline, firstly along the Baltic coast of Germany, onwards past the Netherlands and across the top of France, with some then ending up on the south coast of Britain. Perhaps they are following a traditional route, imprinted into the genetic code, taking in large wetlands as stopping-off points, some still present, others long gone. Britain’s passage population is tiny compared to the larger numbers that turn up in northern France and the Channel Islands. Occurrences in Britain are undoubtedly influenced by the